Conferences come in two types - the ones that are cheap (to attract average people) and the ones that are super expensive (that corporations pay to send staff to).
E.g. the blackhat security conference in las vegas cost $2900 usd.
That's the other aspect - a thousand dollar ticket isn't that large a part of the price if you also have to fly everyone in and get hotels for multiple days (and probably a nice hotel in an expensive location)
I dunno man, I can go to a 4 day music festival that costs like $250-$300 for the weekend, I'm sure that the budget for the performers is a hell of a lot more than whatever the budget for the speakers at this event is.